Amplifying device for microwaves



Dec. 21,1954

R. H. SVENSSON 2,697,799

AMPLIFYING DEVICE FOR MICROWAVES Filed Dec. 1, 1948 i1 2 '6 F- I FIG. 1.

7 Q Q INVENTOR. 7'

Al 1m MNARHQLMFRIDSVNSON FIG f a ATTORNEYS United States PatentAMPLIFYING DEVICE FOR MICROWAVES Regnar Holmfrid Svensson,Hammarbyhojden, Sweden,

assignor to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden, acompany of Sweden Application December 1, 1948, Serial No. 62,809

6 Claims. (Cl. 31539) The present invention refers to an amplifyingdevice for micro-waves. Electromagnetic waves, especially waves with ashort wave-length, so called micro-waves, have the particularity, thatthey readily follow the surface of metallic conductors. A micro-wave,which is caught by a wave-guide, can be made to follow a helically woundmetallic wire outgoing from such a wave-guide. It is known to enclose ahelically wound metallic wire in a high evacuated glass tube togetherwith an electron gun emitting an electron beam along the axis of thehelix towards a collecting anode. If the pitch and length of each turnof the helix is chosen so that micro-waves following the surface of themetallic wire are propagated along the axis of the helix with the samespeed as the electrons in the electron beam, the micro-waves willactuate the electrons in the electron beam and these will, due toelectrostatic induction, produce an amplified electromagneticoscillation having the wave-length of the incoming micro-waves, whichoscillation can be collected by a wave-guide at the farthest end of thehelix.

It is not necessary to wind the metallic wire conducting the micro-wavesas a helix, it can also be formed as a plane wave-shaped line in whichthe pitch and length of the individual waves is such that the componentof ad vance of the micro-waves along the axis of the line substantiallycorresponds in velocity to that of the electron beam, or consist of azig-zag-shapcd cutting in a sheetmetal band, along which the electronbeam from the electron gun passes at the rate just defined.

The present invention refers to an amplifying device for micro-waves, inwhich the micro-waves are made to follow a curved conductor enclosed inan evacuated receptacle.

A tube according to the invention is provided with an elongatedelectron-emitting cathode arranged inside the evacuated receptaclealongside the conductor and with its axis parallel to the axis of theconductor. When working this tube is arranged in a magnetic fieldperpendicular to the axis of the cathode. The electrons produced by thecathode are forced by the magnetic field to move along the axis of thecathode with a speed corresponding to the speed with which themicro-waves proceed along the axis of the cathode. They are thusinfluenced by the micro-waves (accelerated or retarded) and may byelectrostatic induction produce an amplified electromagnetic wave havingthe same wave-length as the micro-waves.

The invention will be more clearly described below wiah reference to theaccompanying Figures 1, 2, 3, .4 an 5.

Fig. 1 shows an application of the invention for the amplification ofmicrowaves entering through a co-axial cable.

Fig. 2 shows a section A-B in Fig. 3 of an amplifying device accordingto the invention.

Fig. 3 shows an application of the invention for the amplification ofmicro-waves caught by a wave-guide.

Fig. 4 shows in plan a wave guide comprising the edges of a sinuous slotin a sheet metal strip.

Fig. 5 is a view similar to Fig. 1 but showing in reduced scale thewhole length and both ends of the amplifying device.

In Figs. 1, 2 and 5, 2 is a highly evacuated glass envelope enclosed ina metal tube 1 screening the amplifylng device from the surroundings.Only half of the amplifying device is shown, since it is symmetricalwith respect to the line A--B. At each end of the glass envelope 2,there is a narrow, fused metallic tube 3, in the center of which anelectron-emitting filament 4 is kept in position by a glass pearl 13sealing the metallic tube 3. The filament 4 is the cathode of the tube.A co-axial cable with an outer conductor 6 and an inner conductor 7 isconnected to each end of the tube. The outer conductors are connected tothe metallic screen 1 and each of the inner conductors connected to theends of a helically wound or wave-shaped wave-guide 8, the axis of whichis parallel to that of the cathode 4 and which reduces the propagationspeed of the micro-waves along the cathode to below the speed of light.The device is arranged in a transverse magnetic field, like that whichappears from Fig. 2, which shows a section of Fig. 3 at AB. 12 is amagnet with the poles N and S. In Fig. 1, there is further animpedance-transformer 9 matched by means of the piston 10, and a piston11 for matching of the metallic screen 1 to the co-axial cable and itstension. The piston 11 consists of two metallic rings insulated fromeach other by means of a cylindrical insulating filler. .One of themetallic rings makes contact with the screen 1 and the other with themetallic tube 3.

The device acts in the following manner. By means of devices, which arenot shown in Fig. 1 but are indicated in Fig. 3 by battery 14, thecathode 4 is given a negative voltage in relation to the conductor 8.Electrons emitted from the cathode 4 are obliged by the magnetic fieldto move along the axis of the cathode toward the right of Fig. 1. Theyform cycloid-like curves. A micro-wave which enters through the co-axialcable, propagates along the conductor 8, which has such a length andpitch of individual wave bends, that the micro-wave will move with acomponent in the longitudinal direction of the tube 2 with substantiallythe same speed as the electrons emitted from the cathode. The micro-wavewill influence the free electrons so that they are accelerated orretarded. If an electron is accelerated, it will return to the cathode,

. but if it is retarded it will continue along the cathode and either goto the conductor 8 or be caught by a collecting anode 20, Fig. 5, at thefar right end of the tube. This collecting anode may otherwise consistof a part of the conductor 8, e. g. one or several narrow windings in ahelix around the cathode 4. ,By electrostatic induction the electronswill react on the micro-wave along the condulftozr 8 so, that it will beamplified when leaving the tu e In order to increase the efficiency ofthe amplifying de- .vice, a focusing electrode 5 in Figs. 1 and 2 isinserted,

which electrode consists of a bar or trough stretching along the cathodeand connected to the same voltage as the cathode or a negative voltagein relation to the cathode. The focusing electrode is placed so that theelectrons are reflected in a direction perpendicular to the magneticfield. The focusing electrode is fixed to and metallically connectedwith the metal tube 3.

Figs. 2-3 show an application of the invention for a radio transmissionsystem with micro-waves. The highly evacuated glass tube 2, the metaltubes 3, the cathode 4, the glass pearl 13, the focusing electrode 5 andthe magnet 12 are the same as in the description of Fig. 1. Fig. 2 showsa section at AB through the device according to Fig. 3. The tube isscreened by two metallic tubes 1a and 1b connected to each other bymeans of flanges between which a metallic plate 7 fused in the wall ofthe glass tube 2 is rigidly fixed. A wave-guide 6 and a short metallictube 9 with an adjustable piston 10 for matching the wave-guide to itsouter impedance are furthermore fastened to the metallic tube 1a. In themetallic tube 1b there is also a piston 11 made as described above forthe piston 11 in Fig. l and intended for matching of the screen 1a--1bto the wave-guide 6. The device is symmetric with regard to the lineA-B, as clearly shown in the small scale view of Fig. 5.

The amplifying device according to Fig. 3 acts in the following manner.A micro-wave, which has been caught by the wave-guide 6, follows theplate 7 and the conductor 8 to a transmitter wave-guide (not shown)corresponding to the wave-guide 6 and arranged at the opposite end ofthe metallic tube 1a. The voltage source 14 keeps the cathode 4 negativein relation to the screens 1a and 1b and the plate 7 and plane, sinuousconductor 8. Electrons emitted from the cathode and caused to proceed incycloid-like curves along the cathode by the magnetic field from themagnet 12 in Fig. 2 are accelerated or retarded by the micro-wavespropagating along the conductor 8. The electrons, which have beenaccelerated, return to the cathode, whilst electrons, which have beenretarded, are caught by a plate corresponding to the plate 7 in Fig. 3in the opposite end of the glass tube 2. Said plate 7 is shaped as acollecting anode. Part of the electrons will part from the cathode tothe conductor 8. By means of electrostatic induction the electrons willamplify the micro-wave proceeding along the conductor 8.

Besides the two embodiments according to Fig. 1 and Fig. 3, combinationscan be obtained by shaping the receiving or emitting half of theamplifying device e. g. according to Fig. 1 and the other half accordingto Fig. 3. It is thus possible to transmit amplified micro-waves from acoaxial cable to an antenna array or to transmit anlljplifiedmicro-waves from an antenna array to a coaxial ca le.

Furthermore the shape of the wave guiding conductor 8 may be changedfrom the helix of Fig. l and the plane, sinuous conductor of Fig. 3 tothe form shown in Fig. 4. Here the micro-waves are guided by the edgesof a sinuous slot 8 in a plane metal strip 16 positioned above thereflecting trough 5 and the cathode 4, in the manner shown for thewaving conductor 8 in Fig. 2. In Fig. 4 the connector plates 7 are shownelectrically connected to the respective ends of the slot 8 in strip 16.

' means outside said receptacle producing a magnetic field perpendicularto said two axes to direct a beam of elec trons from the cathodeparallel to said axes and between the cathode and wave guide, means fordelivering microwaves to one end of said guide for passage therealong,means to take off amplified micro-waves from adjacent the other end ofthe wave guide, the length and pitch of the curves of the wave guideconductor being such that 1 the component of advance of the micro-wavesparallel with said axes corresponds substantially to the rate of travelof the electronbeam along said axes.

2. The electron discharge apparatus as claimed in claim 1 in which saidwave guide comprises the edges of a sinuous slot in a sheet metal striplying wholly in a plane parallel to the direction of the magnetic field.

3. An electron tube for amplification of micro-waves comprising, incombination, a plane surface wave guide for micro-waves having waveshaped edges disposed about an axis of symmetry in said surface, anelectron emitting cathode having an axis extending parallel to said axisof the guide and in all parts adjacent to said guide, a troughlikefocussing electrode extending longitudinally of and adjacent to saidcathode, an evacuated receptacle enclosing said guide, said cathode andsaid focussing electrode, means outside said receptacle producing amagnetic field perpendicular to said axis and said cathode and parallelto said surface to cause a beam of electrons emitted from said cathodeto propagate along said axis between the cathode and the said guide,means delivering micro-waves to one end of said guide for passagetherealong and means leading away the micro-waves from the other end ofthe guide, the pitch and length of the individual Waves of said edgesbeing such that the component of advance of the micro-waves along saidaxes substantially corresponds in velocity to that of the electron beam.

4. In an electron tube for amplification of micro-waves as claimed inclaim 3, said guide for micro-waves consisting of a zig-zag shapedconductor.

5. The electron discharge apparatus as claimed in claim 3 wherein saidwave guide lies wholly in a plane surface parallel to the direction ofthe magnetic field.

6. The electron discharge apparatus as claimed in claim 1 5 in whichsaid guide comprises a conductor outlining the slnuous wave form.

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